This invention relates to a method for returning the movable part of a machine tool which has position control to the original point.
A machine tool, such as a cartoning machine, etc., a guide section, hot melt tank, flap-folding tucker, emboss coder, etc. is made adjustable in respect to its width and height in order to cope with the volume of a variety of cartons. For instance, external threads engageable with internal threads provided in the guide section can be rotated by a servo motor thereby shifting the guide section. The shifting of any movable part is generally done after it has been returned to the original point. The frame of a machine body, for example, is generally regarded as the plane in which the original point is set. In this case, a normally closed switch is provided on the frame. When a movable part approaches the frame to a prescribed extent (this is taken as the original point of the movable part), the normally closed switch is opened. The movable part stops shifting in response to the opening of the switch, thereby effecting its return to the original point.
If the movable part is quickly drawn near the frame in order to shorten the length of time required to return the movable part, the part fails to stop instantly, even if the switch is opened. Therefore, the movable part is undesirably brought back to a point beyond the specified original point, thereby preventing return of the movable part from being precise. Conversely, if the precise return of the movable part is attempted, the movable part must approach the frame slowly, thereby requiring a longer period of time.